NAME

       sd_bus_message_new, sd_bus_message_ref, sd_bus_message_unref, sd_bus_message_unrefp,
       SD_BUS_MESSAGE_METHOD_CALL, SD_BUS_MESSAGE_METHOD_RETURN, SD_BUS_MESSAGE_METHOD_ERROR,
       SD_BUS_MESSAGE_SIGNAL, sd_bus_message_get_bus - Create a new bus message object and create
       or destroy references to it

SYNOPSIS

       #include <systemd/sd-bus.h>

       enum {
             SD_BUS_MESSAGE_METHOD_CALL,
             SD_BUS_MESSAGE_METHOD_RETURN,
             SD_BUS_MESSAGE_METHOD_ERROR,
             SD_BUS_MESSAGE_SIGNAL,
       };

       int sd_bus_message_new(sd_bus *bus, sd_bus_message **m, uint8_t type);

       sd_bus_message *sd_bus_message_ref(sd_bus_message *m);

       sd_bus_message *sd_bus_message_unref(sd_bus_message *m);

       void sd_bus_message_unrefp(sd_bus_message **mp);

       sd_bus *sd_bus_message_get_bus(sd_bus_message *m);

DESCRIPTION

       sd_bus_message_new() creates a new bus message object attached to the bus bus and returns
       it in the output parameter m. This object is reference-counted, and will be destroyed when
       all references are gone. Initially, the caller of this function owns the sole reference to
       the message object. Note that the message object holds a reference to the bus object, so
       the bus object will not be destroyed as long as the message exists.

       Note: this is a low-level call. In most cases functions like
       sd_bus_message_new_method_call(3), sd_bus_message_new_method_error(3),
       sd_bus_message_new_method_return(3), and sd_bus_message_new_signal(3) that create a
       message of a certain type and initialize various fields are easier to use.

       The type parameter specifies the type of the message. It must be one of
       SD_BUS_MESSAGE_METHOD_CALL — a method call, SD_BUS_MESSAGE_METHOD_RETURN — a method call
       reply, SD_BUS_MESSAGE_METHOD_ERROR — an error reply to a method call,
       SD_BUS_MESSAGE_SIGNAL — a broadcast message with no reply.

       The flag to allow interactive authorization is initialized based on the current value set
       in the bus object, see sd_bus_set_allow_interactive_authorization(3). This may be changed
       using sd_bus_message_set_allow_interactive_authorization(3).

       sd_bus_message_ref() increases the reference counter of m by one.

       sd_bus_message_unref() decreases the reference counter of m by one. Once the reference
       count has dropped to zero, message object is destroyed and cannot be used anymore, so
       further calls to sd_bus_message_ref() or sd_bus_message_unref() are illegal.

       sd_bus_message_unrefp() is similar to sd_bus_message_unref() but takes a pointer to a
       pointer to an sd_bus_message object. This call is useful in conjunction with GCC's and
       LLVM's Clean-up Variable Attribute[1]. See sd_bus_new(3) for an example how to use the
       cleanup attribute.

       sd_bus_message_ref() and sd_bus_message_unref() execute no operation if the passed in bus
       object address is NULL.  sd_bus_message_unrefp() will first dereference its argument,
       which must not be NULL, and will execute no operation if that is NULL.

       sd_bus_message_get_bus() returns the bus object that message m is attached to.

RETURN VALUE

       On success, sd_bus_message_new() returns 0 or a positive integer. On failure, it returns a
       negative errno-style error code.

       sd_bus_message_ref() always returns the argument.

       sd_bus_message_unref() always returns NULL.

       sd_bus_message_get_bus() always returns the bus object.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           Specified type is invalid.

       -ENOTCONN
           The bus parameter bus is NULL or the bus is not connected.

       -ENOMEM
           Memory allocation failed.

NOTES

       These APIs are implemented as a shared library, which can be compiled and linked to with
       the libsystemd pkg-config(1) file.

SEE ALSO

       systemd(1), sd-bus(3), sd_bus_new(3), sd_bus_message_new_method_call(3),
       sd_bus_message_new_method_error(3), sd_bus_message_new_method_return(3),
       sd_bus_message_new_signal(3)

NOTES

        1. Clean-up Variable Attribute
           https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html